Surely peace is only the yang aspect. If we're going to have peace we need to be prepared to make war. I have no doubt that if either the UK or the US decided to disband its military we would have one of the largest wars the world has ever seen. I'm sure you'll all disagree with me, but if you pursue the negative and ignore the positive yin and yang will surely be out of balance.

Back to the original question; I think Sun Tzu is just dealing with the practicalities of war i.e. it is a very costly business whether you ultimately win or loose.

I must admit I don't know enough about O'Sensei to say whether he would have said anything like that. However it certainly has the christian ethic behind it - you try telling that to people who are about to get wiped out in acts of genocide (such as the kurds) and I think they may feel differently.